Overload protective switch



May 1952 c. l. HALL ET AL OVERLOAD PROTECTIVE SWITCH Filed Dec. 21, 1946by Wm Their Attorney.

n e. @K w h In M mi m w s in ch 0 d 1 a I. 533 a; H M w Patented May 6,1952 UNITED STATES OVERLOAD PROTECTIVE SWITCH Chester I. Hall, VischersFerry, and-John L. Slonneger, Alplaus, N. Y., assignors to GeneralElectric Company, a corporation of New York Application December 21,1946, Serial No. 717,710

4 Claims. 1

Our invention relates to control devices, and more particularly tocurrent responsive thermal overload protective relays for electricapparatus, such as electric motors, and has for its object a reliablerelay that is shock-resisting, is compensated for changes in ambienttemperature, is readily adaptable to a variety of A.-C. and D.-C.current ratings, is quick acting in response to current changes, can bequickly and easily reset, and inherently safeguards the circuit in caseof a failure of its operating or compensating members.

In carrying out our invention we provide an expansible containerprovided with a movable wall, free to move in response to changes influid pressure, filled with a vaporizable liquid, and directly connectedthrough a small opening to a small container constituting a boiler,which is also filled with the vaporizable liquid. We provide a controlmember operated by the movement of the movable wall and a means ofheating the container constituting a boiler. In order to compensate forchanges in ambient temperature we provide a second container with amovable wall, free to move in response to changes in fluid pressure,filled with a liquid-vapor mixture, and positioned so that its expansionopposes the expansion of aforesaid container.

For a more complete understanding of our invention, reference should behad to the accompanying drawing in which Fig. 1 is an elevational viewof a thermal relay embodying our invention; Fig. 2 is a sectional viewtaken along the line 22 of Fig. 1 looking in the direction of thearrows; Fig. 3 is a sectional view taken along the line 33 of Fig. 1looking in the direction of the arrows; Fig. 4 is a sectional view takenalong the line 4-4 of Fig. 1 looking in the direction of the arrows; andFig. 5 is an enlarged perspective view of a latch disk and rod, guidesfor the bellows, and a part of a latch plunger member.

Referring to the drawing, our invention in one form comprises as anoperating member a suitable expansible container provided with a movablewall, such as a low spring rate expansible bellows I, guided at itslower end by a plastic guide 2, and at its upper end connected to aplastic insulation plate 3. The plate 3 bears against a metal holdingstrip 4 which is connected to a plastic case 5 by screws 6 and 1 and toa plastic back or cover 8 by other screws (not shown). The bellows I isdirectly connected to a small boiler 9 by a tube ID of small diameter.The assembly is completely filled with a suitable vaporizable liquid,such as trichlorotrifiuoroethane (F113) or acetone, and sealed, therebymaintaining equal fluid pressure in the bellows I and the boiler 9. Asseen in Fig. 2 the bellows I is thermally insulated from the boiler 9 bythe air gap formed by the cylindrical space II, except for theconduction through the small tube I0.

Consequently the tube I0 is made just large enough to allow readyequalization of fluid pressure, but small enough to minimize conductionof heat, between the boiler 9 and the bellows I. Preferably the tube II!is formed of a metal having favorable high temperature characteristics,such as that known commercially as Nichrome. The boiler 9 is just largeenough relative to the bellows I so that vaporization of part of thecontained liquid, such as acetone, will force sufiicient liquid from.the boiler 9 into the bellows I to operate a latch tripping mechanismhereinafter described, but small enough to prevent overstraining thebellows I in case the boiler 9 is sufiiciently heated that all of theliquid contained within it is vaporized.

After the acetone in the boiler 9 reaches its vaporization temperaturethe expansion of the vapor is rapid, and sufficient liquid acetone isquickly forced into the bellows I to actuate suitable electric circuitcontrol means described be- ,low. Until the acetone in the boiler 9reaches its vaporization temperature, however, its expansion is soslight that it has substantially no eiiect upon the volume of acetone inthe bellows I and consequently does not cause appreciable move ment ofthe operating member. This sudden action feature constitutes one of theinherent shock-resisting characteristics of our invention as theoperating member remains in its closed position until a predeterminedheat rise is effected in the boiler 9. Moreover without a transfer ofheat to the boiler the acetone will not vaporize. Thus for the shorttime duration of a physical shock substantially no liquid acetone willvaporize as it will receive no appreciable transfer of heat. Anytendency of the free end of the bellows i to move toward its tripactuating position as a result of a shock will be counteracted by thereduction in fluid pressure within the bellows I and the boiler 9. Thenthe pressure of the atmosphere upon the bellows I will force the freeend to return to its previous position. The small orifice connection,consisting of the tube Ill, between the boiler 9 and the bellows Ifurther serves to dampen any movement of the free end of the bellows iby preventing a sudden transfer of liquid from the boiler 9 to thebellows I. Thus the effect of a shock would be to move the free end ofthe bellows I less toward the trip position than if the nichrome tube Itwere larger. These shock resisting features are also inherentcharacteristics of our invention.

Means for heating the boiler 9 is provided in the form of an electricalresistance type removable heater I2. A heating element I3, preferablyformed of Nichrome or the like, is spring loaded against the top of theboiler 9, as shown in Fig. 2. The heater I2 is attached to the plasticcase 5 by screws I4 and I5 as shown in Fig. 1, and connected to thepower circuit by connector lugs l6 and I1 and contact screws Hi and |9.The removable heater [2, while of simple design, makes this applicationof our invention adaptable to motors and circuits of both A.-C. andD.-C. power of current ratings varying from A; to 100 amperes. Thedesign of the heater element [3 making the transfer surface as large asthe top of the boiler 9 makes for quick response of our relay to changesin the current density in the heater l2.

A latch tripping mechanism is provided including a cylindrical latchmember 2|! with a projecting flange or disk 2| on its lower end and aguide rod 22 on which the latch member is slidably mounted. The trippingmechanism further includes a spring biased plunger 23 with a plate 24and an aperture 25. It can best be understood with reference made toFigs. 3 and 5. The rod 22 is secured at its upper end by a screw to theguide 2 of the bellows I, a washer 22 being interposed between them. Theaperture 25 of the plate 24 is slightly larger than the projecting disk2| and may have, as shown in Figs. 3 and 5 a small slot 26 just largeenough to accommodate the shank portion of the latch member 20. Theplunger plate 24 is guided on three sides by the guide slot 21, and isnormally held in the right hand position shown in Figs. 2 and 4 by thelatch disk 2|. The maximum travel of the plunger is indicated by theposition in Fig. 5, which shows the latch member 20 in the lower or tripposition and the plunger plate 24 in its left hand circuit breakingposition.

The operation of the latch tripping mechanism can be explained withreference to Figs.

4 and 5. Upon expansion of the bellows l the latch member 28 is forceddownward, and when the latch disk 2i disengages the plate 24, theplunger moves quickly with a snap action to the left as shown on thedrawing under the bias of the spring 28 until it reaches the positionshown in Fig. 5. Means are provided by which the lateral movement of theplunger 23 in its biased direction opens the control circuit byreleasing the pressure exerted by a switch or contact bar 29 on twostrips 30, made of a conducting spring metal such as spring bronze. Thetwo contact buttons on the switch bar 29 thereupon are released fromcontact with the corresponding buttons on the spring bronze strips 30,which in turn move to the left, as seen in Fig. 4 in accordance withtheir bias. The two contact buttons on a contact bar 3|, as shown inFig. 4, are normally in contact with two corresponding contact points onthe bronze strips 30, and the contacts are opened upon movement of thebronze strips 33 following release of the restraining force of theswitch bar 29. By the positioning of the two contact bars 29 and 3| weprovide an additional shock resisting feature, since a physical shocktending to jar either one of the strips 30 away from one of its contactbars will cause it to bear upon the other contact bar with acorrespondingly greater force. Thus an open circuit resulting from ashock is very unlikely. The contact bar 3| is fixed to the plastic case5 by screws 32. The spring bronze strips 30 are fixed to the case 5 byscrews 33 as shown in Fig. 1 and Fig. 4. We provide external connectorscrews 34 and 35 as shown in Fig. 1 and Fig. 4. With no contact betweenbronze strips 30 and either contact bar 29 or 3|, the external connectorscrews 34 and 35 of the control circuit are deenergized and the powercircuit thereupon opened by the usual relay means. We further provide ametal guide plate 36 held against the bellows guide 2 and a lowerbellows guide 31 by the outside edges of the frame 5. The guide 36serves to keep the latch rod 22 perpendicular to the plunger plate 24.

To compensate for changes in ambient we provide a suitable containerwith a movable wall, such as a low spring rate expansible bellows 38,filled with a liquid and vapor mixture of a vaporizable liquid such asmethyl bromide or ethyl chloride. One end of the bellows 38 is free tomove in response to changes in fluid pressure and the other end bearsagainst the flat metal holding strip 5. The compensating bellows 38 isguided by the guide 31, and its movable end upon expansion exerts anupward pressure on the latch member guide rod 22 to the lower end ofwhich the guide 31 is secured whereby this pressure is transmitted tothe bellows guide 2 and through it on the bellows A spring 40 locatedbetween the bellows guide 31 and the latch disk 2| exerts a pressurewhich biases the latch member 20 upward into engagement with the washer22', and limits the upward force exerted by the projecting disk 2| onthe plunger plate 24 when the plate 24 is in the position shown in Fig.5.

An increase in ambient causes the pressure of the ethyl chloride to riseand thereby causes the bellows 38 to expand. Said expansion exertspressure through latch rod 22 on the bellows I, thus raising thevaporization temperature of the acetone in the boiler 9. If the springrates of the bellows and the bellows 33 are set so as to be equal whenthe latch member 28 is in the release position, then the acetone in theboiler 9 will vaporize in suflicient quantity to cause the latch member20 to move to the release position when the vapor pressure in the boiler9 just exceeds the vapor pressure in the bellows 38. For thus balancingthe spring rates of the bellows and 38 we provide a factory adjustmentscrew 4| as shown in Fig. 2 and Fig. 4. since the boiling point ofacetone for any given pressure, ranging from zero to seventy pounds persquare inch gage, is approximately 45 C. above that of ethyl chloride atthe equivalent pressure, the temperature at which the relay will tripwill be approximately 45 C. above ambient. Thus the compensating bellows38 has as its object to cause the plunger 23 to be released at apredetermined temperature rise, i. e., a predetermined current densityin the heater element |3, regardless of ambient changes. Moreover afurther shock resisting feature is added by the effect of the bellows38. If the bellows moves toward its latch releasing position because ofshock this movement will be opposed by the bellows 38. The vaporpressure within the bellows 38 will be increased with such movement ofthe bellows and thus will add to the force of the atmosphere inreturning the bellows to its normal position. The latch mechanism 20,2|, 23, and 24 is arranged to safeguard the power circuit in case of afailure of, or leak in, either bellows or 38. Upon failure of thebellows the vapor pressure of ethyl chloride in bellows 38 will force upthe latch disk 2| of latch member 28 until its clears the top of theplate 24 of plunger 23, the spring 28 thereupon forcing open the plunger23 and opening the control circuit contacts. Upon failure of bellows 38,the force which it normally exerts will be reduced, which in turn willreduce the rated current of the relay by reducing the vaporizationtemperature of the acetone in the boiler 9.

An inherent feature of our invention is its quick reset characteristic.After the heat of vaporization of the acetone in the boiler 9 isreached, some acetone vaporizes and forces liquid acetone into thebellows as described before. Consequently, after release of the plunger23, the bellows l is completely filled with cool, liquid acetone, whilethe boiler 9 contains hot acetone vapor. Upon condensation of a slightamount of the hot acetone vapor, a drop in pressure in the boiler 9results, and cool liquid acetone enters the boiler 9 to equalize thepressure in the bellows l and the boiler 9. This action causes immediateadditional condensation in the boiler by chilling the acetone vaportherein, thus causing more liquid acetone to enter the boiler 9 from thebellows I. The condensation of the acetone vapor is rapid because theliquid acetone from the bellows I continues to chill it until the boiler9 is again completely filled with liquid acetone. Then resetting ispossible by pressing in the plunger 23 to allow the aperture 25 of theplunger plate 24 to become aligned with the disk 2| of the latch member20.

Resetting time is further shortened by the addition of a wedge-likeprojection 42 on the top of the plunger plate 24, making it just highenough to push the bellows guide 2 up several mils when the guide 2 isin the tripped position as shown in Fig. 5. This forces a small quantityof liquid acetone into the boiler 9 to chill the hot vapor more quicklythan it normally would cool and condense, and will be helpful in caseour invention is applied to a relay use requiring exceptionally quickresetting.

While we have shown a particular embodiment of our invention, it will beunderstood, of course, that we do not wish to be limited thereto, sincemany modifications may be made, and we therefore contemplate by theappended claims to cover any such modifications as fall within the truespirit and scope of our invention.

What we claim and desire to secure by Letters Patent of the UnitedStates is:

1. A thermal overload protective device for an electric circuitcomprising, a first sealed expansible container containing a vaporizableliquid and having a first rectilinearly movable wall, a second sealedexpansible container containing a thermally expansible vapor underpressure and having a second rectilinearly movable wall dis posed inopposing relation with respect to said first wall, means rigidlyconnecting said walls together, electric heating means disposed tovaporize said liquid in response to excessive flow of current in saidcircuit, switching means adapted to interrupt said circuit, a memberbiased for movement transversely of the direction of movement of saidconnected walls to actuate said switching means to circuit interruptingposition, and latching means connected to said movable walls andengaging said member when said walls are in a normal intermediateposition to restrain circuit interrupting movement of said member, saidlatching means disengaging said member upon movement of said walls ineither direction, whereby said circuit is interrupted upon failure ofeither of said containers.

2. A thermal overload protective device for an electric circuitcomprising, a first expansible bellows containing a vaporizable liquidand having a first rectilinearly movable end wall, a second expansiblebellows containing a thermally expansible vapor under pressure andhaving a second rectilinearly movable end wall, means connecting saidend walls together in fixed spaced apart opposing relation, electricheating means for vaporizing said liquid to expand said first bellows inresponse to excessive fiow of current in said circuit, switching meansadapted to interrupt said circuit, means including a fiat plate biasedfor movement transversely of the direction of movement of said movablewalls, to actuate said switching means to circuit opening position, andlatching means carried; by said connecting means and disposed inedgewise latching engagement with said flat plate when said movablewalls are in a normal position with said liquid unvaporized, wherebysaid plate is released to interrupt said circuit, upon vaporization ofsaid liquid or upon failure of either of said bel lows.

3. A thermal overload protective device for an electric circuitcomprisin a pair of expansible bellows disposed in end-to-end relationwith their adjacent end walls connected together for rectilinearmovement in opposing relation, a vaporizable liquid in one of saidbellows, a thermally expansible vapor in the other of said bellows,electric heating means for vaporizing said liquid in response to flow ofexcessive current in said circuit, switching means adapted to interruptsaid circuit, and latching means for retaining said switching means in acircuit closing position comprising a fiat plate biased for edgewisemovement transversely of the direction of movement of said end walls anda detent normally engaging said plate in edgewise relation and connectedto be disengaged from said plate in response to movement of said endwalls in either direction.

4. A thermal overload protective device for an electric circuitcomprising a base, a pair of expansible bellows disposed in end-to-endopposing relation with their remote end walls fixed to said base, a rodconnecting the movable adjacent end walls of said bellows forrectilinear movement in fixed spaced apart relation, a vaporizableliquid in one of said bellows, a thermally expansible vapor in the otherof said bellows, electric heating means for vaporizing said liquid inresponse to the flow of a predetermined excessive current in saidcircuit, switching means adapted to interrupt said circuit, means foractuating said switching means to circuit opening position including anapertured plate loosely embracing said rod and biased for edgewisemovement perpendicular to said rod, and a fiat latching plate mountedupon said rod and disposed for edgewise latching engagement in saidaperture when said liquid is in an unvaporized state.

CHESTER I. HALL. JOHN L. SLONNEGER.

REFERENCES CITED The following references are of record in the file ofthis patent:

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